The present invention relates to methods and apparatus for image segmentation and image registration. In particular, it relates to segmentation and registration of medical 2D and 3D images that are acquired at different phases and/or at different times. Imaging applications for oncology follow-up studies have just recently been introduced to the clinical workflow. Cancer treatment has also become an extraordinary important procedure in today's healthcare due to cancer being among the most frequent causes of death. Monitoring the patient's response to radiation treatment by investigating cancer development is crucial for determining success or failure of the therapy. One indicator for cancer development is the change in size and structure of lesions found in thorax and abdomen that can be imaged by contrast enhanced CT, as shown in FIG. 1 images 101 and 103. CT images are acquired by well known computed axial tomography (CAT) or computed tomography (CT) scan techniques.
Contrast-enhanced multi-phase CT refers to CT acquisitions at different phases determined by the time of contrast agent injection, i.e. native, arterial, venous, late, etc. phase. Not only the size of the lesion but also the way the contrast agent is being washed-in and washed-out in the lesion is an indicator for the stage of cancer. As each contrast phase varies dramatically in the amount of contrast agent that is visible in the image, the ability to detect and segment those lesions becomes extremely challenging in some phases for a segmentation application operating on a computer and even for the human eye. Note, that lesions are not visible in CT without contrast agent, i.e. native phase. Follow-up studies may include two consecutive CT multiphase acquisitions taken before and after treatment and usually within a 3 months time span. To this end, there may be up to 8 or more volumes, i.e. about 4 volumes per multi-phase information. Segmenting of lesions should preferably be performed in all phases of all follow-up studies.
FIG. 1 shows a contour outline 102 in image 101 and, in image 103, diameter measurement indicators 104 of a lesion in the liver imaged at the venous phase of contrast enhanced CT.
One of the challenges is heavily varying contrast between the phases. Another challenge is the apparent deformations of objects between the follow-up studies. The deformations result from tissue and organ changes due to radiation treatment, breathing motion, cancer evolvement, lesion changes, different patient position, etc. Current methods for cancer monitoring in follow-up studies focus on the segmentation part in baseline and follow-up volume and establishing lesion correspondence afterwards.
It is believed that currently there are no known methods or apparatus to model lesion segmentation and correspondence simultaneously in a combined framework. Accordingly, novel and improved methods and apparatus are required to provide simultaneous segmentation and registration of objects in different but related images.